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Re: RDF Semantics: corrections

From: pat hayes <phayes@ihmc.us>
Date: Wed, 14 Jan 2004 11:26:04 -0600
Message-Id: <p06001f05bc2b2a068576@[]>
To: Graham Klyne <GK@ninebynine.org>
Cc: www-rdf-comments@w3.org

>At 22:07 13/01/04 -0600, pat hayes wrote:
>>One way to extend this is to require that the class extension of x 
>>be a *subset* of the value space of x.  This seems to be the 
>>minimal extension which would handle datatype clashes 
>>appropriately.  But now, the finite-value class examples give 
>>difficulties for completeness arguments, since now the 'boolean' 
>>example is rejuvenated:
>>a p "true"^^boolean
>>a p "false"^^boolean
>>c type boolean
>>a p c
>>In order to block this, we would need to allow ICEXT(I(boolean)) to 
>>be a proper superset of the boolean value space.
>>It can't be both a subset and a proper superset.
>My apologies for not following the debate closely enough, but I'm 
>not sure what is the problem here.  Why would one want to "block" 
>this entailment?

Because such an entailment makes it impractical to have a complete 
system of rules in the RDF/RDFS style for D-entailment: in effect, it 
encodes a universal quantification (if p(a true) and p(a false) then 
forall x if boolean(x) then p(a x) ).  One can of course add this as 
a 'special' rule for xsd:boolean, but then you need a special rule 
for any finite datatype.  One can make out a reasonable case that 
such universals are alien to the RDF conjunction-existential way of 
doing things; and Herman noticed that the weaker semantics would 
allow a completeness result to be obtained. This weaker semantics 
allows literal type-checking but doesn't handle any kind of 
'exclusion' reasoning on datatype classes. I was seduced by the 
appeal of having a D-entailment lemma, but now see that not being 
able to recognize type clashes is too high a price to pay.

(Pat retires to his corner to lick his wounds.)


>Graham Klyne
>For email:

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Received on Wednesday, 14 January 2004 12:26:07 UTC

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